GMAT数学精解--算术概述(3)
<p> 1.平均数</p><p> 2.中数</p><p> <span word="TO">TO</span> <span word="CALCULATE">CALCULATE</span> <span word="THE">THE</span> <span word="MEDIAN">MEDIAN</span> <span word="OF">OF</span> <span word="N">N</span> <span word="NUMBERS">NUMBERS</span>，<span word="FIRSTSGROUPSTHE">FIRSTSGROUPSTHE</span> <span word="NUMBERS">NUMBERS</span> <span word="FROM">FROM</span> <span word="LEAST">LEAST</span> <span word="TO">TO</span> <span word="GREATEST">GREATEST</span>;<span word="IF">IF</span> <span word="N">N</span> <span word="IS">IS</span> <span word="ODD">ODD</span>，<span word="THE">THE</span> <span word="MEDIAN">MEDIAN</span> <span word="IS">IS</span> <span word="DEFINED">DEFINED</span> <span word="AS">AS</span> <span word="THE">THE</span> <span word="MIDDLE">MIDDLE</span> <span word="NUMBER">NUMBER</span>，<span word="WHILE">WHILE</span> <span word="IF">IF</span> <span word="N">N</span> <span word="IS">IS</span> <span word="EVEN">EVEN</span>，<span word="THE">THE</span> <span word="MEDIAN">MEDIAN</span> <span word="IS">IS</span> <span word="DEFINED">DEFINED</span> <span word="AS">AS</span> <span word="THE">THE</span> <span word="AVERAGE">AVERAGE</span> <span word="OF">OF</span> <span word="THE">THE</span> <span word="TWO">TWO</span> <span word="MIDDLE">MIDDLE</span> <span word="NUMBERS">NUMBERS</span>. <span word="FOR">FOR</span> <span word="THE">THE</span> <span word="DATA">DATA</span> 6, 4, 7, 10, 4, <span word="THE">THE</span> <span word="NUMBERS">NUMBERS</span>, <span word="IN">IN</span> <span word="ORDER">ORDER</span>, <span word="ARE">ARE</span> 4, 4, 6, 7, 10, <span word="AND">AND</span> <span word="THE">THE</span> <span word="MEDIAN">MEDIAN</span> <span word="IS">IS</span> 6, <span word="THE">THE</span> <span word="MIDDLE">MIDDLE</span> <span word="NUMBER">NUMBER</span>. <span word="FOR">FOR</span> <span word="THE">THE</span> <span word="NUMBERS">NUMBERS</span> 4, 6, 6, 8, 9, 12, <span word="THE">THE</span> <span word="MEDIAN">MEDIAN</span> <span word="IS">IS</span> /2 = 7. <span word="NOTE">NOTE</span> <span word="THAT">THAT</span> <span word="THE">THE</span> <span word="MEAN">MEAN</span> <span word="OF">OF</span> <span word="THESE">THESE</span> <span word="NUMBERS">NUMBERS</span> <span word="IS">IS</span> 7.5.</p><p> 3.众数：一组数中的众数是指出现频率最高的数。</p><p> 例：<span word="THE">THE</span> <span word="MODE">MODE</span> <span word="OF">OF</span> 7，9，6，7，2，1 <span word="IS">IS</span> 7。</p><p> 4.值域：表明数的分布的量，其被定义为最大值减最小值的差。</p><p> 例：<span word="THE">THE</span> <span word="RANGE">RANGE</span> <span word="OF">OF</span>1，7，27，27，36 <span word="IS">IS</span> 36-= 37。</p><p> 5.标准方差：</p><p> <span word="ONE">ONE</span> <span word="OF">OF</span> <span word="THE">THE</span> <span word="MOST">MOST</span> <span word="COMMON">COMMON</span> <span word="MEASURES">MEASURES</span> <span word="OF">OF</span> <span word="DISPERSION">DISPERSION</span> <span word="IS">IS</span> <span word="THE">THE</span> <span word="STANDARD">STANDARD</span> <span word="DEVIATION">DEVIATION</span>. <span word="GENERALLY">GENERALLY</span> <span word="SPEAKING">SPEAKING</span>, <span word="THE">THE</span> <span word="GREATER">GREATER</span> <span word="THE">THE</span> <span word="DATA">DATA</span> <span word="ARE">ARE</span> <span word="SPREAD">SPREAD</span> <span word="AWAY">AWAY</span> <span word="FROM">FROM</span> <span word="THE">THE</span> <span word="MEAN">MEAN</span>, <span word="THE">THE</span> <span word="GREATER">GREATER</span> <span word="THE">THE</span> <span word="STANDARD">STANDARD</span> <span word="DEVIATION">DEVIATION</span>. <span word="THE">THE</span> <span word="STANDARD">STANDARD</span> <span word="DEVIATION">DEVIATION</span> <span word="OF">OF</span> <span word="N">N</span> <span word="NUMBERS">NUMBERS</span> <span word="CAN">CAN</span> <span word="BE">BE</span> <span word="CALCULATED">CALCULATED</span> <span word="AS">AS</span> <span word="FOLLOWS">FOLLOWS</span>:</p><p> <span word="FIND">FIND</span> <span word="THE">THE</span> <span word="ARITHMETIC">ARITHMETIC</span> <span word="MEAN">MEAN</span> ;</p><p> <span word="FIND">FIND</span> <span word="THE">THE</span> <span word="DIFFERENCES">DIFFERENCES</span> <span word="BETWEEN">BETWEEN</span> <span word="THE">THE</span> <span word="MEAN">MEAN</span> <span word="AND">AND</span> <span word="EACH">EACH</span> <span word="OF">OF</span> <span word="THE">THE</span> <span word="N">N</span> <span word="NUMBERS">NUMBERS</span> ;</p><p> <span word="SQUARE">SQUARE</span> <span word="EACH">EACH</span> <span word="OF">OF</span> <span word="THE">THE</span> <span word="DIFFERENCES">DIFFERENCES</span> ;</p><p> <span word="FIND">FIND</span> <span word="THE">THE</span> <span word="AVERAGE">AVERAGE</span> <span word="OF">OF</span> <span word="THE">THE</span> <span word="SQUARED">SQUARED</span> <span word="DIFFERENCES">DIFFERENCES</span> ;</p><p> <span word="TAKE">TAKE</span> <span word="THE">THE</span> <span word="NONNEGATIVE">NONNEGATIVE</span> <span word="SQUARE">SQUARE</span> <span word="ROOT">ROOT</span> <span word="OF">OF</span> <span word="THIS">THIS</span> <span word="AVERAGE">AVERAGE</span>.</p>
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